1. Field of the Invention
The present invention relates to a device for binary-coding a read signal from a magnetic tape, and more particularly to a device for binary-coding a read signal from a magnetic tape, which is suitable for a half inch cartridge magnetic tape drive (hereinafter referred to as "1/2 CGMT device").
2. Description of the Related Art
Up to now, in the 1/2 CGMT device, a waveform read from a magnetic tape where data has been recorded through the NRZI rule (non return to zero in-change rule) is differentiated and read. A position of data "1" represented by the read waveform is a positive or negative peak of the read waveform, and the magnetic defect on a medium and an electric external noise cause the read waveform to be undesirably changed. In other words, they cause the insertion of false data which is called "drop-in" and the deletion of data which is called "drop-out" to be generated.
For the above reason, a digital data read circuit is structured such that, in order to set a condition where the amplitude of the analog read signal is a given level or more in detection of data "1", an absolute value of the amplitude of the read waveform is detected, a peak of a given threshold voltage is detected, and the detected peak is set to data "1".
However, in the above conventional example, a difference in read waveform is caused depending on the respective read heads and magnetic tape medium because the characteristic of the read heads and the characteristic of the magnetic tape medium are dispersed. Therefore, in case of an analog read waveform shown in FIG. 5a, there was a case where error digital data shown in FIG. 5c might be read without reading correct digital data shown in FIG. 5b. The reason is because the threshold voltage is fixed.